In recent years, people have much been concerned about the environment. Particularly, water which has an intimate relation to their living has been a matter of primary concern.
Harmful matters such as organic matters, ammonia, and so forth, and matters which may cause odors and colors are contained in secondary sewage treatment water, secondary night soil treatment water, industrial waste water, tap water, small water supply system water, exclusive tap water, water for industrial use, wastewater recycling system water, and effluents from fish farms and culture ponds.
Accordingly, it is necessary to treat water highly. Various water treatment methods have been investigated. Especially, contamination of rivers with phenol type organic matters is a great concern. Anxiety has been directed to nonyl phenols or nonyl phenol isomers regarded as estrogen which causes troubles as environmental hormone.
The nonyl phenol isomers are produced while chemical substances contained in surfactants and so forth are decomposed in rivers. The phenol type organic matters have a benzene ring and can not easily be decomposed by heating and so forth. By addition of chlorine, the decomposition becomes possible. However, when the phenol type organic matters are decomposed with chlorine added, undesired chlorides are formed.
As to such treatment of water as described above, a water treatment method using ozone is well known. For removal of harmful matters, odor matters, and color matters by oxidative decomposition, and for pasteurization, this method is widely used.
For the purpose of enhancing the oxidation decomposition rate of harmful matters in water with ozone, that is, the treatment rate of the water, there is known a method for adding a surfactant whereby the contact between foul water and ozone is increased, as stated in Japanese Unexamined Patent Publication No. 52-8650.
As generally known, the oxidative reaction of ozone in water is due to the direct-contact reaction of an ozone molecule, and the hydroxyl radical (OH.) and the hydroperoxy radical (HO.sub.2.) produced by the self-decomposition of ozone. Particularly, the hydroperoxy radical (HO.) has a higher oxidation capacity. The increase of hydroperoxy radicals increase the efficiency of the reaction.
The following methods for accelerating the above reaction are well known: the pH value of water to be treated is enhanced; hydrogen peroxides are added; ultraviolet rays are irradiated; radiation is applied; supersonic waves are applied; catalysts such as metal ions, metal oxides, and so forth are used; and so forth.
In addition, there is a well-known method for treating foul water with ozone in the presence of a phenol, benzoic acid, and dodecyl benzensulfonic acid as a catalyst. For example, such a method is stated in Japanese Unexamined Patent Publication No. 06-23377.
However, in the above-described techniques, ozone is relatively expensive, and the oxidative decomposition rate of ozone is low. Accordingly, water treatment at a high efficiency is realized with difficulty only by introducing water under treatment into a large-scale reaction tank, and injecting ozone.
According to the method of adding a surfactant, as stated in Japanese Unexamined Patent Publication No. 52-8650, the reaction is accelerated by increasing the area of reaction sites. When lots of organic matters exist in water under treatment, the surfactant may be absorbed by the organic matters in the water, so that the frothing capacity is reduced. If the amount of the surfactant is increased in order to compensate for the reduced frothing capacity, lots of foam will be generated, which probably causes troubles in working.
According to the method for treating foul water with ozone in the presence of a phenol, benzoic acid, or dodecy benzenesulfonic acid, as stated in Japanese Unexamined Patent Publication No. 06-23377, it is difficult to treat foul water with ozone sufficiently efficiently in the presence of the catalyst.